Method of fabricating an SrRuO3 film

ABSTRACT

A method of fabricating an SrRuO 3  thin film is disclosed. The method utilizes a multi-step deposition process for the separate control of the Ru reagent, relative to the Sr reagent, which requires a much lower deposition temperature than the Sr reagent. A Ru reagent gas is supplied by a bubbler and deposited onto a substrate. Following the deposition of the Ru reagent, the Sr liquid reagent is vaporized and deposited onto the Ru layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to the field of thin dielectricfilms. More specifically, the invention relates to the formation of anSrRuO₃ film by deposition utilizing independent deposition segments foreach of the dissimilar precursor compositions.

[0003] 2. Description of the Related Art

[0004] Barium strontium titanate, BaSrTiO₃ is one of the most promisingcandidates as a dielectric material for post-1-Gbit dynamic randomaccess memory capacitors. However, as device sizes continue to shrink,the thickness of the dielectric must be reduced in order to increase theaccumulated charge capacitance and reduce the capacitor area,. In thindielectric films with thickness on the order of several tens of nm, alow leakage current and a higher dielectric constant are required.However, when a dielectric is made very thin, unwanted changes, such asan increase in leakage current and a decrease in the dielectric constantrelative to the bulk, may occur. Although the origins of these phenomenaare not completely understood, they are known to depend greatly on thematerials used for the capacitor electrodes.

[0005] Currently, there are numerous possible candidates for theelectrodes used in BaSrTiO₃ capacitors, including Pt, Ir, Ru and RuO2.However, SrRuO₃ is one of the most promising candidates for an electrodematerial having an improved performance with respect to capacitance,leakage degradation and lattice match for BaSrTiO₃.

[0006] In the formation of thin films, layers and coatings onsubstrates, a wide variety of source materials have been employed. Thesesource materials include reagents and precursor materials of widelyvarying types, and in various physical states. To achieve highly uniformthickness layers of a conformal character on the substrate, vapor phasedeposition has been used widely. In vapor phase deposition, the sourcematerial may be of initially solid form which is sublimed or melted andvaporized to provide a desirable vapor phase source reagent.Alternatively, the reagent may be of normally liquid state, which isvaporized, or the reagent may be in the vapor phase in the firstinstance. Conventionally, these reagents may be used in mixture with oneanother in a multicomponent fluid which is utilized to deposit acorresponding multicomponent or heterogeneous film material such asSrRuO₃. Such advanced thin film materials are increasingly important inthe manufacture of microelectronic devices and in the emerging field ofnanotechnology. For such applications and their implementation in highvolume commercial manufacturing processes, it is essential that the filmmorphology, composition and stoichiometry be closely controlled. This inturn requires highly reliable and efficient methods for deposition ofsource reagents to the locus of film formation.

[0007] Various technologies well known in the art exist for applyingthin films to substrates or other substrates in manufacturing steps forintegrated circuits (ICs). For instance, Chemical Vapor Deposition (CVD)is a often-used, commercialized process. Also, a relatively newtechnology, Atomic Layer Deposition (ALD), a variant of CVD, is nowemerging as a potentially superior method for achieving uniformity,excellent step coverage, and transparency to substrate size. ALDhowever, exhibits a generally lower deposition rate (typically about 100ang/min) than CVD (typically about 1000 ang/min).

[0008] Chemical vapor deposition (CVD) is a particularly attractivemethod for forming thin film materials such as SrRuO₃ because of theconformality, composition control, deposition rates and microstructuralhomogeneity. Further, it is readily scaled up to production runs and theelectronics industry has a wide experience and an established equipmentbase in the use of CVD technology which can be applied to new CVDprocesses. In general, the control of key variables such as stoichometryand film thickness and the coating of a wide variety of substrategeometries is possible with CVD. Forming the thin films by CVD permitsthe integration of SrRuO₃ into existing device production technologies.

[0009] ALD, although a slower process than CVD, demonstrates aremarkable ability to maintain ultra-uniform thin deposition layers overcomplex topology. This is at least partially because ALD is not fluxdependent as CVD processes are. In other words, CVD requires specificand uniform substrate temperature and precursors to be in a state ofuniformity in the process chambers in order to produce a desired layerof uniform thickness on a substrate surface. This flux-independentnature of ALD allows processing at lower temperatures than withconventional CVD processes.

[0010] However, in either case, when the film being deposited is amulticomponent material, such as SrRuO₃, rather than a pure element,controlling the deposition of the film is critical to obtaining thedesired film properties. In the deposition of such materials, which mayform films with a wide range of stoichiometries, the controlled deliveryof the source reagents into the reactor chamber is essential.

[0011] The present invention is directed to controlling the delivery ofsource reagents into the reactor chamber to produce thin films ofSrRuO₃.

SUMMARY OF THE INVENTION

[0012] The present invention is directed to a method of fabricating anSrRuO₃ thin film. The method utilizes a multi-step deposition processfor the separate control of the Ru reagent, relative to the Sr reagent,which requires a much lower deposition temperature than the Sr reagent.

[0013] A Ru reagent gas is supplied by a bubbler and deposited onto asubstrate at temperatures below 200° C. Following the deposition of theRu reagent, the Sr liquid reagent is vaporized and deposited onto the Rulayer at temperatures above 200° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing and other advantages and features of the inventionwill become more apparent from the detailed description of the inventiongiven below with reference to the accompanying drawings in which:

[0015]FIG. 1 is a schematic representation of an apparatus according tothe present invention as employed for the fabrication of an SrRuO₃ film;

[0016]FIG. 2 is a schematic representation of a multiple layer filmformed utilizing SrRuO₃ fabricated in accordance with a method of thepresent invention; and

[0017]FIG. 3 illustrates in block diagram form a processor based systemincluding a memory device employing a capacitor having a conductorformed of an SrRuO₃ film fabricated in accordance with a method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described as set forth in FIGS.1-3. Other embodiments may be utilized and structural or logical changesmay be made without departing from the spirit or scope of the presentinvention. Although the invention is illustrated in the drawings inconnection with CVD processes, the invention may also be practiced usingALD processes as well. In general, the invention may be applicablewherever deposition is utilized for the deposition of SrRuO₃ thin films.Like items are referred to by like reference numerals.

[0019] The term “substrate” used in the following description mayinclude any semiconductor-based structure that has an exposed siliconsurface. Structure must be understood to include silicon-on insulator(SOI), silicon-on sapphire (SOS), doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductorfoundation, and other semiconductor structures. The semiconductor neednot be silicon-based. The semiconductor could be silicon-germanium,germanium, or gallium arsenide. When reference is made to substrate inthe following description, previous process steps may have been utilizedto form regions or junctions in or on the base semiconductor orfoundation.

[0020] Referring now to the drawings, FIG. 1 illustrates a reactionchamber 39 coupled by a precursor feed line 17 and branch feed line 21further connecting to a bubbler 1. Bubbler 1 comprises a reaction vessel5 containing the Ru precursor or reagent, such as tricarbonyl (1-3cyclohexadiene) ruthenium (Ru), ruthenium acetylacetonate, ruthenocene,triruthenium dodecacarbonyl or tris(2,2,6,6-tetramethyl-3,5-heptanedionato) ruthenium, which is connectedto a gas carrier vessel 3, by a carrier feed line 7. The gas carriervessel 3 contains a carrier gas such as Ar, He, N₂, CO or any othergases inert to a Ru precursor for effecting the transport of the vaporprecursor Ru to the reaction chamber 39. The reaction vessel 5 ismaintained at a temperature of about 25° C. The reaction vessel 5 isalso coupled to an exhaust or bypass line 4 containing flow controlvalve 6, whereby the flow of precursor vapor may be bypassed from thereaction chamber. Further, branch feed line 21 is provided with flowcontrol valve 15 therein which may be selectively opened or closed toflow the precursor to the reaction chamber 39 or to terminate the flowof precursor vapor to the reactor by closure of the valve. Flow controlvalve 15 may also be partially opened to regulate the flow therein ofthe precursor vapor.

[0021] Further, as shown in FIG. 1 the precursor feed line 17 is alsocoupled to branch feed line 23 connecting to the vaporizer unit 20.Vaporizer unit 20 has an interior volume 25 therein containing avaporizer element 22 for effecting vaporization of the liquid precursorsuch as, Sr(2,2,6,6-tetramethyl-3,5-heptanedionate)₂(“Sr (THD)”₂), or Srbis(triisopropylcyclopentadienyl), flowed to the vaporizer unit forvaporization of the precursor therein to form precursor vapor. Vaporizerbranch line 23 is provided with flow control valve 19 therein, which maybe selectively opened or closed to flow the precursor to the reactionchamber 39 or to terminate the flow of precursor vapor to the reactor byclosure of the valve. The vaporizer unit 20 is also coupled to anexhaust or bypass line 29 containing flow control valve 27, whereby theflow of precursor vapor may be bypassed from the reaction chamber 39.Flow control valve 19 may also be partially opened to regulate the flowthere through of the precursor vapor.

[0022] Vaporizer 20 receives liquid Sr precursor in line 31, having pump33 disposed therein. As used herein, the term “pump” is intended to bebroadly construed to include all suitable motive fluid driver means,including, without limitation, pumps, compressors, ejectors, eductors,mass flow controllers, pressure-building circuits, peristaltic drivers,and any other means by which fluid may be conducted through conduit,pipe, line or channel structures. Supply vessel 37 containing liquid Srprecursor (for instance, Sr (THD)₂in a solution of about 0.1 M butylacetate) is coupled by line 31 to pump 33 which receives the Srprecursor and flows the precursor to vaporizer unit 20 in line 31.

[0023] Hence, the vaporized precursors are flowed from the bubbler 1 andvaporizer unit 20 in precursor feed line 17 to the reaction chamber 39,in which the precursor vapors of Ru and Sr are contacted with asubstrate 43 on support 41 to deposit a film of the desired character,and with spent precursor vapor being exhausted from the reaction chamber39 in line 45, for recycle, treatment or other disposition thereof.

[0024] With the FIG. 1 arrangement, the Ru precursor is first depositedon substrate 43 in reaction chamber 39 which is maintained at a pressureof about 0.5-10 torr, preferably around 3 torr. The substrate 43 surfacetemperature is maintained at about 150° C.-600° C., preferably attemperatures below 200° C. The Ru precursor is deposited to a thicknessof about 50-500A and the quantity of the Ru precursor gas is maintainedat about 30-50 sccm. The deposition time is approximately 2-10 minutes.

[0025] After deposition of a Ru precursor, the Sr precursor is depositedon substrate 43 in reaction chamber 39 which is maintained at a pressureof about 0.5-10 torr, preferably around 3 torr. The substrate 43 surfacetemperature is maintained at about 325° C.-700° C., preferably attemperatures above 200° C. The Sr precursor is deposited to a thicknessof about 50-500A and the quantity of the Sr precursor gas is maintainedat about 30-50 sccm. The deposition time is around 1-4 minutes.Following the deposition of Ru and Sr, a post annealing process isperformed at a temperature about 550° C.-850° C. for about 10 seconds toabout 30 minutes, preferably around 700° C. for about 30 seconds.

[0026] Thus, the present invention provides a unique, independent methodof depositing each of the components necessary for the fabrication of anSrRuO₃ film. Accordingly, separate control of the Ru reagent whichrequires a much lower deposition temperature than Sr reagent is therebyfacilitated, for the purpose of optimizing the SrRuO₃ film formationprocess to yield a desired SrRuO₃ film on the substrate 43 in thereaction chamber 39.

[0027]FIG. 2 is a schematic representation of a container capacitor 200for memory cells, said capacitor having SrRuO₃ conductor fabricatedaccording to the present invention. A first insulating layer 201provides electrical isolation for underlying electronic devices such asthin film field effect transistors (FETs). A second insulating layer(not shown) is formed over the first insulating layer 201, and a viaetched through the second insulating layer which may act as a templatefor the container capacitor 200. Via walls are lined with a conductivematerial 203, namely SrRuO₃ film fabricated by the method of the presentinvention. A planarizing etch is conducted to remove excess SrRuO₃ overthe top surface of the second insulating layer. The remaining secondinsulating layer may then be etched away to expose an outside surface205. The SrRuO₃ film 203 represents the bottom or storage electrode ofthe container capacitor 200. A thin dielectric layer 207 is then formedover SrRuO₃ film 203, followed by a second conductive layer 22 (e.g.,also SrRuO₃ film), which represents the top or reference electrode forthe container capacitor 200. By following the contours of thethree-dimensional container structure, the effective electrode surfacearea is substantially increased, allowing for substantially greatercapacitance. Also, contact is made between the container capacitor 200and an underlying active area 211 of the semiconductor substrate 213between narrowly spaced transistor gates 215 (e.g., DRAM word lines), asshown in FIG. 2. The actual contact is made by a contact conductive plug217 which can be formed prior to formation of the container capacitorstructure.

[0028] A typical processor based system which includes a memory device,e.g. RAM 460 containing capacitor having SrRuO₃ conductors fabricatedaccording to the present invention is illustrated generally at 400 inFIG. 3. A computer system is exemplary of a system having integratedcircuits, such as for example memory circuits. Most conventionalcomputers include memory devices permitting storage of significantamounts of data. The data is accessed during operation of the computers.Other types of dedicated processing systems, e.g., radio systems,television systems, GPS receiver systems, telephones and telephonesystems also contain memory devices which can utilize the presentinvention.

[0029] A processor based system, such as a computer system 400, forexample, generally comprises a central processing unit (CPU) 410, forexample, a microprocessor, that communicates with one or moreinput/output (I/O) devices 440, 450 over a bus 470. The computer system400 also includes the random access memory (RAM) 460, read only memory(ROM) 480 and may include peripheral devices such as a floppy disk drive420 and a compact disk (CD) ROM drive 430 which also communicate withCPU 410 over the bus 470. RAM 460 preferably has storage capacitor whichincludes SrRuO, conductors formed as previously described with referenceto FIG. 1. It may also be desirable to integrate the processor 410 andmemory 460 on a single IC chip.

[0030] While preferred embodiments of the invention have been describedand illustrated above, it should be understood that these are exemplaryof the invention and are not to be considered as limiting. Additions,deletions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description but is only limited by the scope of the appendedclaims.

What is claimed as new and desired to be protected by letters patent ofthe united states is:
 1. A method of fabricating an SrRuO₃ film,comprising: depositing a first component of said film on a substrate ata first temperature; depositing a second component of said film on saidsubstrate at a second temperature higher than said first temperaturewherein said deposition of said second component is performed separatelyfrom said first component; and annealing said first and secondcomponents to form an SrRuO, thin film.
 2. The method of claim I whereinsaid deposition of said first and second components is performed by CVD.3. The method of claim 1 wherein said deposition of said first andsecond components is performed by ALD.
 4. The method of claim 1 whereinsaid first component is selected from the group consisting oftricarbonyl (1-3 cyclohexadiene) ruthenium (Ru), rutheniumacetylacetonate, ruthenocene, triruthenium dodecacarbonyl or tris(2,2,6,6-tetramethyl-3,5-heptanedionato) ruthenium.
 5. The method ofclaim 1 wherein said second component is selected from the groupconsisting of Sr(2,2,6,6-tetramethyl-3,5-heptanedionate)₂, or Srbis(triisopropylcyclopentadienyl).
 6. The method of claim 1 wherein saidfirst temperature is about 150° C.-600° C.
 7. The method of claim 1wherein said first temperature is less than 200° C.
 8. The method ofclaim 1 wherein said second temperature is about 325° C.-700° C.
 9. Themethod of claim 1 wherein said second temperature is higher than 200° C.10. The method of claim 1 wherein said first component is deposited to athickness of about 50-500A.
 11. The method of claim 1 wherein saidsecond component is deposited to a thickness of about 50-500A.
 12. Themethod of claim I wherein said first component is deposited for about2-10 minutes.
 13. The method of claim 1 wherein said second component isdeposited for about 1-4 minutes.
 14. The method of claim 1 wherein saidfirst and second component is deposited at a pressure of about 0.5-10torr.
 15. The method of claim 1 wherein said deposition of said firstcomponent comprises the use of a bubbler to generate a first vaporcomponent.
 16. The method of claim 15 wherein said bubbler utilizes a Hecarrier.
 17. The method of claim 15 wherein said bubbler utilizes an Arcarrier.
 18. The method of claim 15 wherein said bubbler utilizes an N₂carrier.
 19. The method of claim 15 wherein said bubbler utilizes an COcarrier.
 20. The method of claim 15 wherein said bubbler utilizes a gasinert to a Ru precursor.
 21. The method of claim 1 wherein saiddeposition of said second component comprises the use of a vaporizer togenerate a second vapor component.
 22. An SrRuO₃ thin film comprising:an annealed film formed from a first component deposited on a substrateat a first temperature and a second component deposited on said firstcomponent at a second temperature higher than said first temperature.23. The device of claim 22 wherein said first component is selected fromthe group consisting of tricarbonyl (1-3 cyclohexadiene) ruthenium (Ru),ruthenium acetylacetonate, ruthenocene, triruthenium dodecacarbonyl ortris (2,2,6,6-tetramethyl-3,5-heptanedionato) ruthenium.
 24. The deviceof claim 22 wherein said second component is selected from the groupconsisting of Sr(2,2,6,6-tetramethyl-3,5-heptanedionate)₂, or Srbis(triisopropylcyclopentadienyl).
 25. The device of claim 22 whereinsaid first component is about 50-500A thick.
 26. The device of claim 22wherein said second component is about 50-500A thick.
 27. A processorbased system comprising: a central processing unit; a memory devicecoupled to said central processing unit to receive data from and supplydata to said central processing unit, said memory device comprising: acapacitor having at least one electrode comprising an annealed film,said annealed film comprising: a first component deposited on asubstrate at a first temperature and a second component deposited onsaid first component at a second temperature higher than said firsttemperature.
 28. The system of claim 27 wherein said first component isselected from the group consisting of tricarbonyl (1-3 cyclohexadiene)ruthenium (Ru), ruthenium acetylacetonate, ruthenocene, trirutheniumdodecacarbonyl or tris (2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium.
 29. The system of claim 27 wherein said second component isselected from the group consisting ofSr(2,2,6,6-tetramethyl-3,5-heptanedionate)₂, or Srbis(triisopropylcyclopentadienyl).
 30. The system of claim 27 whereinsaid first component is about 50-500A thick.
 31. The system of claim 27wherein said second component is d about 50-500A thick.